Chemical Formula

NaFe3+Si2O6

Hardness (Mohs)

6-6.5

Crystal System

Monoclinic

Streak

Greyish-green to brownish-black

Luster

Vitreous to sub-metallic

Diaphaneity

Translucent to opaque

Color

Greenish-black, black, dark green, brown

Crystal Habit / Mode of Occurrence

Prismatic, often long and slender crystals; acicular, fibrous, granular, massive